Supported vanadia catalyst and use thereof for nitrile production

ABSTRACT

Vanadia supported on a silica-alumina or gamma-alumina support in an amount to provide a vanadia to support weight ratio ranging from about 0.3:1 to about 3:1 substantially entirely within the pores of the support, the vanadia having been placed in molten form substantially within the pores of a support having a surface area greater than about 50 m 2  gram, a porosity greater than about 0.4 cc/gram which further includes an alkali metal, with the vanadium metal to alkali metal mole ratio being from 2:1 to 30:1. At least a portion of the alkali metal is preferably in the form of alkali metal vanadate. The catalyst is used for the production of nitriles from a compound containing at least one alkyl group.

This application is a division of U.S. Pat. application Ser. No. 819,771filed on July 28, 1977, and now U.S. Pat. No. 4,092,271, with theaforesaid application being a continuation in part of U.S. Pat.application Ser. No. 727,060, filed on Sept. 27, 1976, and nowabandoned.

This invention relates to a supported vanadia catalyst and the usethereof for the production of nitriles.

U.S. Pat. No. 3,963,645 discloses a supported vanadia catalyst whereinthe vanadia is supported on a silica-alumina or gamma-alumina support inan amount to provide a metal oxide to support weight ratio ranging fromabout 0.3:1 to about 3:1 substantially entirely within the pores of thesupport, with the vanadia having been placed in molten form within thepores of the support which has a surface area greater than about 50 m²/gram and a porosity greater than about 0.4 cc/gram. The supportedvanadia catalyst is particularly suitable for the production of nitrilesby oxidative ammonolysis (ammoxidation). The present invention isdirected to an improvement in the supported vanadia catalyst of theaforesaid patent, and the use of such an improved catalyst for theproduction of nitriles.

In accordance with the present invention, there is provided a catalystof vanadia supported on a porous support in an amount to provide avanadia to support weight ratio ranging from about 0.3:1 to about 3:1substantially entirely within the pores of the support, with the vanadiahaving been placed in molten form substantially within the pores of asupport having a surface area greater than about 50 m² /gram, a porositygreater than about 0.4 cc/gram, with the catalyst further containing analkali metal in an amount to increase the catalytic effect of thecatalyst.

More particularly, the catalyst includes an alkali metal which is eitherlithium, sodium, potassium, rubidium or cesium, in an amount to providea vanadium metal to alkali metal mole ratio of from about 2:1 to 30:1,and preferably from about 8:1 to 20:1. The alkali metal is preferablysodium.

The support on which the vanadium pentoxide is to be supported has asurface area of greater than about 50 m² /gram and a porosity greaterthan about 0.4 cc/gram. In general, the surface area of the support isno greater than about 600 m² /gram and the porosity is no greater thanabout 1.2 cc/gram. Supports having a surface area of about 200 m² /gramhave been found to provide particularly good results. As representativeexamples of preferred supports having such properties there may bementioned: silica-alumina, zeolites, alumina, including microcrystallineand the γ, δ, η, κ and χ modifications of alumina. The silica-aluminaand gamma-alumina supports are particularly preferred.

The fused supported vanadia catalyst which is promoted with an alkalimetal may be conveniently prepared by mixing the support with an aqueoussolution of the alkali metal hydroxide to provide the desired amount ofalkali metal in the support. The support containing the alkali metal isthen mixed with vanadia and heated to above the fusion point of thevanadia to draw the vanadia into the pores of the alkali metal treatedsupport.

As an alternative, the supported vanadia catalyst may be prepared by afusion technique without initial treatment of the support with an alkalimetal, followed by impregnation of the supported vanadia catalyst withan aqueous solution of the alkali metal hydroxide to provide therequired amount of alkali metal, and heating to above the fusion pointof vanadia.

As another alternative, the vanadia and an alkali metal compound such asthe hydroxide or oxide, may be preblended in the appropriate amounts byprocedures known in the art and the resulting blend supported on thesupport by the fusion technique.

The general technique for supporting the vanadium pentoxide within thepores of a porous support is described in U.S. Pat. No. 3,963,645.

In accordance with a preferred embodiment of the present invention, aparticularly active form of the catalyst is produced by providing amixture of alkali metal hydroxide and vanadia on the support and heatingthe supported mixture to the fusion temperature of the vanadia at acontrolled heating rate. More particularly, the supported mixture isheated to the vanadia fusion temperature at an average rate of less than20° F./minute, preferably less than 15° F./minute, with a particularlypreferred heating rate being 10° F./minute or less. Thus, in general,the supported mixture is heated up to the fusion temperature over a timeperiod of at least 1 hour, with particularly good results being achievedover a period of 2 hours or more.

The supported mixture is maintained at or above the fusion temperaturefor a time sufficient to place the vanadia substantially entirely withinthe pores of the support. In general, the supported mixture ismaintained at a temperature of from 1300° F. to 1450° F. for a timeperiod of from 1 to 10 hours.

In preparing the catalyst in accordance with the preferred procedure,i.e., controlled heating of vanadia and alkali metal hydroxide on thesupport, at least a portion of the alkali metal is present in the finalcatalyst as the alkali metal vanadate; preferably sodium vanadate. Ifthe heating to fusion temperature is effected at a more rapid rate,alkali metal vanadate is not formed and such a catalyst has been foundto be less selective for the production of nitriles, even though it isan improvement over the fused catalyst without the alkali metal. Thus,in accordance with the particularly preferred embodiment, the catalystincludes both vanadia and alkali metal vanadate, preferably sodiumvanadate. In general, at least 10% by weight of the alkali metal ispresent as the vanadate.

The supported vanadia catalyst of the present invention is particularlysuitable for the production of nitriles by oxidative ammonolysis(ammoxidation). The organic reactant employed as a starting material forthe production of nitriles by ammoxidation is a compound including atleast one alkyl group; namely, aromatic, aliphatic, alicyclic andheterocyclic compounds having at least one alkyl group.

As representative examples of alkyl substituted aromatic hydrocarbonswhich are suitable as starting materials, there may be mentioned thealkyl substituted benzenes and naphthalenes, and in particular, benzenewhich may contain two or more alkyl groups in which case the resultingproduct is a polynitrile. The alkyl group generally contains no morethan 4 carbon atoms, preferably no more than 2 carbon atoms. Asparticular examples of suitable alkyl substituted aromatic hydrocarbons,there is: toluene; various xylenes to produce the variousphthalonitriles; ethyl benzene, trimethyl benzenes, methylnaphthalenes,durene and the like.

As representative examples of suitable aliphatic compounds, there may bementioned: olefinic hydrocarbons having at least one alkyl group, suchas propylene and isobutylene to produce acrylonitrile andmethacrylonitrile, respectively.

As representative examples of suitable alicyclic compounds, there may bementioned: methylcyclopentane, methylcyclohexane, the alkyl substituteddecalins, and the like.

The heterocyclic compounds useful as starting materials for producingnitriles by ammoxidation in accordance with the present inventioninclude alkyl substituted furans, pyrroles, indoles, thiophenes,pyrazoles, imidazoles, thiazoles, oxazoles, pyrans, pyridines,quinolines, isoquinolines, pyrimidines, pyridazines, pyrazines and thelike. The preferred heterocyclic compounds are the alkyl, preferablylower alkyl, substituted pyridines, with pyridines having an alkyl groupin a beta-position with respect to the heterocyclic nitrogen atom beingparticularly preferred in that such pyridines can be converted tonicotinonitrile; in particular, 3-picoline, 2,3-and2,5-dimethylpyridine, 2-methyl-5-ethylpyridine and 3-ethylpyridine.

The starting material, containing at least one alkyl group is convertedto a nitrile by contacting the starting material with ammonia, in thevapor phase, in the presence of the supported vanadia catalyst of thepresent invention, either in the absence or presence of a free oxygencontaining gas, preferably in the absence of a free oxygen containinggas. The contacting is generally effected at a temperature from about300° C. to about 500° C., preferably from about 375° C. to about 475°C., with the contact time generally ranging from about 0.5 to about 15seconds, preferably from about 2 to about 8 seconds. Reaction pressuresgenerally range from about 1 to about 5 atmospheres. The mole ratio ofammonia to starting material generally ranges from about 2:1 to about16:1, preferably from about 3:1 to about 8:1. If an oxygen-containinggas is employed in the feed, the gas is employed in an amount such thatthe quantity of oxygen and starting material in the feed is outside ofthe explosive range.

In accordance with the preferred embodiment of the invention, thestarting material and ammonia are contacted with the supported vanadiacatalyst of the present invention in the absence of oxygen, with thesupported vanadia catalyst being periodically passed to another reactor(in general the supported vanadia catalyst is not maintained on streamfor a period greater than about 30 minutes, preferably from about 2 toabout 10 minutes), and contacted therein with a free oxygen containinggas to effect regeneration of the catalyst, generally at a time periodfrom about 2 to about 20 minutes. The supported vanadia catalyst is thenrecycled to a nitrile production zone. It is believed that the supportedvanadia catalyst is reduced during the nitrile production step and,consequently, periodic oxidation thereof is required to maintain thesupported vanadia catalyst in the oxidized form necessary for thenitrile production.

The invention will be further described with respect to the followingexamples; however, it is to be understood that the scope of theinvention is not to be limited thereby.

EXAMPLE I Catalyst A (Present Invention)

3000 g. of silica-alumina fluid bed catalyst support (Grace 135) wasslurried in 4500 g. of lwt. % NaOH and agitated for 30 minutes. Aftersettling, the supernatent liquid was decanted and replaced with 4500 g.of water, and the mixture agitated for another 30 minutes. The mixturewas again separated by decantation. After drying at 110° C., the treatedsupport contained 0.9 wt. % Na. This support was then blended with 2000g. of powdered vanadia and heated at 1400° F. for 5 hours in a slowlyrotating cylindrical kiln. After cooling, the catalyst was removed fromthe kiln and screened through a 40 mesh screen.

Catlyst B

3000 g. of a silica-alumina fluid bed catalyst support (Grace 135) wasblended with 2000 g. of powdered vanadia and heated at 1400° F. for 5hours in a slowly rotating cylindrical kiln. After cooling, the catalystwas removed from the kiln and screened through a 40 mesh screen.

Catalysts A and B were then employed for the production ofisophthalonitrile under the following conditions. The ammoxidation waseffected in the absence of molecular oxygen with catalysts A and B beingregenerated in a separate regenerator by contact with oxygen.

                  TABLE I                                                         ______________________________________                                        Catalyst Type        B         A                                              ______________________________________                                        Reactor Pressure, PSIG                                                                             10        10                                             Reactor Temp., °F.                                                                          800       800                                            Regenerator Temp., °F.                                                                      910-930   910-930                                        Catalyst circulation, gms/min.                                                                     56        53                                             Organic Feed Rate/cc/min.                                                                          3.3       3.4                                            Feed Composition                                                              m-xylene, wt. %      69        69                                             M-toluonitrile, wt. %                                                                              31        31                                             NH.sub.3 In feed                                                              mol/mol. organic feed                                                                              9.1       8.8                                            Inert gas in feed                                                             mol/mol. organic feed                                                                              9.4       8.9                                            Conversion, mol %    52.5      41.5                                           Ultimate Yield of Isophthalonitrile                                           Basis m-xylene, mol %                                                                              80.7      86.6                                           Basis ammonia, mol % 27        40                                             ______________________________________                                    

Improved results are obtained by using the catalyst of the presentinvention (Catalyst A) as evidenced by increased ammonia and hydrocarbonyield.

EXAMPLE II Catalyst A (Present Invention)

3000 g. of a silica-alumina fluid bed catalyst support (Grace 135) wasslurried in 4500 g. of lwt. % NaOH and agitated for 30 minutes. Aftersettling, the supernatent liquid was decanted and replaced with 4500 g.of water, and the mixture agitated for another 30 minutes. The mixturewas again separated by decantation. After drying at 110° C., the treatedsupport contained 0.9 wt. % Na. This support was then blended with 2000g. of powdered vanadia and heated at the rate of 10° F./minute in aslowly rotating cylindrical kiln to a temperature of 1400° F. andmaintained at such temperature for 5 hours. After cooling, the catalystwas removed from the kiln and screened through a 40 mesh screen.

In Runs A & B, the catalyst is employed for production ofterephthalonitrile from p-xylene, and nicotinonitrile frombeta-picoline, respectively. The ammoxidation was effected in theabsence of molecular oxygen, with catalysts being regenerated in aseparate regenerator by contact with oxygen.

                  TABLE II                                                        ______________________________________                                                         A        B                                                   ______________________________________                                        Reactor Pressure, PSIG                                                                           25.0       15.0                                            Reactor Temp., °F.                                                                        800        775                                             Regenerator Temp., °F.                                                                    935-955    935-955                                         Catalyst circulation, gms/min.                                                                   112.8      73.8                                            Organic Feed Rate, cc/min.                                                                       6.7        8.0                                             NH.sub.3 in feed                                                              mol/mol. organic feed                                                                            7.8        5.0                                             Inert gas in feed                                                             mol/mol. organic feed                                                                            0.7        0.6                                             Conversion, mol %  50.67      30.05                                           ______________________________________                                    

In Run A the following selectivities and yields are achieved:

    ______________________________________                                        Terephthalonitrile                                                                             93.53                                                        p-tolunitrile    0.00                                                         benzonitrile     0.04                                                         carbon oxides    6.43                                                         Yields, mole %                                                                Ultimate Organic 93.53                                                        Ammonia          65.71                                                        ______________________________________                                    

In Run B, the following selectivities and yields are achieved:

    ______________________________________                                        Selectivity, mole %                                                           Nicotinonitrile   89.66                                                       Pyridine          0.74                                                        Carbon Oxides     9.60                                                        Yields, mole %                                                                Ultimate Organic  89.66                                                       Ammonia           66.70                                                       ______________________________________                                    

EXAMPLE III

Two catalysts are prepared as described with reference to Example II,(40% vanadia and 1% sodium) except that one catalyst was heated at therate of 10° F./min. and the second at a rate of greater than 20° F./min.

In Runs A and B of Table III the catalysts are employed for producingisophthalonitrile from m-xylene. The ammoxidation is effected in theabsence of molecular oxygen, and regeneration of the catalyst iseffected on a cyclic basis rather than by continuous circulation of thecatalyst, as in the previous examples.

                  TABLE III                                                       ______________________________________                                        Run                  A         B                                              ______________________________________                                        Heating Rate for catalyst, °F./min.                                                         >20       10                                             Temperature, °F.                                                                            800       800                                            Catalyst Charge, g   400       400                                            Cat./OH, g/cc        20.8      20                                             Pressure, psig       5         5                                              GHSV (STP), h.sup.-1 1040      1242                                           NH.sub.3 /Organic, mol/mol                                                                         5.4       6                                              Selectivites, mol %                                                           IPN                  56.5      64.9                                           m-TN                 33.9      22.3                                           BN                   --        1.7                                            CO.sub.x             9.5       11.1                                           Conversion, %        37.2      47.4                                           Ultimate Yield, %    85.4      83.8                                           Space-Time Yield, g/gh                                                                             0.15      0.20                                           ______________________________________                                    

The catalyst produced by slow heating provides improved selectivity interms of conversion of methyl group to nitrile.

The present invention is an improvement over the catalyst of U.S. Pat.No. 3,963,645 in that the catalyst of the present invention, whenemployed for the production of nitriles, provides improved hydrocarbonselectivity and ammonia yield. Although Applicant does not intend to belimited by theoretical reasoning, it is believed that the improvedcatalytic effect results from a modification of the vanadia by reactionwith the alkali metal at the fusion temperature.

Numerous modifications and variations of the present invention arepossible in light of the above teachings and, therefore, within thescope of the appended claims, the invention may be practiced otherwisethan as particularly described.

What is claimed is:
 1. In a process for producing a nitrile by thecatalytic ammoxidation of a compound containing at least one alkyl groupconvertible to a nitrile group by reaction with ammonia in the presenceor absence of gaseous oxygen, the improvement comprising:effecting saidammoxidation with a catalyst comprising vanadia supported on a poroussupport in an amount to provide a vanadia to support weight ratioranging from about 0.3:1 to about 3:1 substantially entirely within thepores of the support, said vanadia having been placed in molten formsubstantially within the pores of a support having a surface areagreater than about 50 m² per gram, a porosity greater than about 0.4 ccper gram, said catalyst containing an alkali metal in an amount toprovide a vanadia metal to alkali metal mole ratio of from 2:1 to 30:1.2. The process of claim 1 wherein the support is silica-alumina.
 3. Theprocess of claim 2 wherein the alkali metal is sodium.
 4. The process ofclaim 3 wherein the vanadia metal to alkali metal mole ratio is fromabout 8:1 to 20:1.
 5. The process of claim 1 wherein the support isgamma-alumina.
 6. The process of claim 5 wherein the alkali metal issodium.
 7. The process of claim 6 wherein the vanadia metal to alkalimetal mole ratio is from about 8:1 to 20:1.
 8. The process of claim 1wherein a portion of the alkali metal is present as alkali metalvanadate.
 9. The process of claim 8 wherein the support issilica-alumina.
 10. The process of claim 9 wherein the alkali metal issodium.
 11. The process of claim 10 wherein the vanadia metal to alkalimetal mole ratio is from about 8:1 to 20:1.
 12. The process of claim 8wherein the support is gamma-alumina.
 13. The process of claim 12wherein the alkali metal is sodium.
 14. The process of claim 13 whereinthe vanadia metal to alkali metal mole ratio is from about 8:1 to 20:1.15. The process of claim 1 wherein the compound is benzene substitutedwith at least one alkyl group.
 16. The process of claim 1 wherein thecompound is a pyridine substituted with at least one alkyl group.
 17. Ina process for producing a nitrile by the catalytic ammoxidation of acompound containing at least one alkyl group convertible to a nitrilegroup by reaction with ammonia in the presence or absence of gaseousoxygen, the improvement comprising:effecting said ammoxidation with acatalyst produced by heating a mixture of an alkali metal hydroxide andvanadia supported on a porous support having a surface area greater thanabout 50 meters square per gram and a porosity greater than about 0.4 ccper gram to the fusion temperature of vanadia at an average rate of lessthan 20° F. per minute, said vanadia and alkali metal hydroxide beingemployed in an amount to provide a vanadia to support weight ratio offrom 0.3:1 to 3:1 substantially within the pores of the support and avanadia metal to alkali metal mole ratio of from about 2:1 to 30:1, andmaintaining the support mixture at vanadia fusion temperature to placethe vanadia substantially entirely within the pores of the support. 18.The process of claim 17 wherein the support is selected from the groupconsisting of gamma-alumina and silica-alumina.
 19. The process of claim18 wherein the support is silica-alumina.
 20. The process of claim 18wherein the support is gamma-alumina.
 21. The process of claim 18wherein the compound is benzene substituted with at least alkyl group.22. The process of claim 18 wherein the compound is a pyridinesubstituted with at least one alkyl group.
 23. The process of claim 15wherein the support is selected from the group consisting ofgamma-alumina and silica-alumina.
 24. The process of claim 16 whereinthe support is selected from the group consisting of gamma-alumina andsilica-alumina.